Rapid and sensitive speciation of inorganic iodine in groundwater by IC-ICP-MS with Ar-CH4 mixed plasma

Abstract

Investigation of the iodine species is important to better understand the sources and mobilization processes of high-iodine groundwater. A fast and sensitive method for the determination of iodate (IO3-) and iodide (I-) in groundwater using an improved ion chromatography method coupled with inductively coupled plasma mass spectrometry (IC-ICP-MS) is described. To shorten the separation time of iodine species, a short anion-exchange column, Dionex AG-19, was examined as the analytical column. Isocratic elution using 30 mM KOH facilitated the chromatographic separation of IO3- and I- within one minute, reducing the time in comparison to previous IC-ICP-MS methods with conventional long IC columns (i.e., Hamilton X-100 or Dionex AS-16) by 90%. Moreover, the low analytical sensitivity of iodine, due to its high ionization potential (10.08 eV), was improved five-fold by addition of small amounts of C4 to the Ar plasma. The detection limit was 0.005 μg L-1 for IO3- and 0.006 μg L-1 for I-, while the relative standard deviation for five injections of 0.2 μg L-1I- or IC3- was 1.2-3.3%. The analytical results for three water standard reference materials were in agreement with the certified values. The proposed method was successfully applied to the determination of I- and I03- in seven shallow groundwater samples collected from the Datong Basin, Northern China. The distributions of the iodine species, differing from mountain front plains to flat alluvial plain regions, indicate that the mobilization process of iodine is associated with complex redox conditions.